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Sea-level rise (SLR) will produce unprecedented changes in tidal marsh systems that already cope with daily tidal fluctuation, disturbances from storms, and salinity changes from droughts and runoff events. Additionally, negative impacts from non-native invasive species may alter marsh plants' ability to respond to SLR stressors like increased inundation and salinity. Increasingly, tidal marsh communities must tolerate both changes in the physical environment from SLR and increased risk of invasion by non-native species. To assess the response of a threatened tidal marsh cordgrass (Spartina foliosa) to both stressors, we implemented a field experiment in San Francisco Bay, CA, USA, exposing cordgrass to a treatment that extended tidal inundation projected with SLR using a recently developed in situ method. At one of two field sites, we also enclosed the cordgrass with or without the invasive European green crab, Carcinus maenas. We found that cordgrass responded negatively to longer inundation, although these effects varied by site and year. In higher inundation treatments, cordgrass survival increased with increasing surface elevation of the plot. Cordgrass survival was lower in the presence of invasive green crabs relative to controls. We did not find interacting effects of responses to increased inundation and invasive species presence, which highlights the need to consider how latent or sequential effects of multiple stressors may affect ecosystems. This study demonstrates significant biological responses to invasive species presence and increased inundation. Evaluating relative effects and timing of multiple stressors, especially those induced by climate change and invasive species, will help us to manage threatened ecological communities in a changing world. [ABSTRACT FROM AUTHOR]

Our study investigated the size at the onset of morphological sexual maturity, sexual size dimorphism, and relative growth in the green porcelain crab Petrolisthes armatus from a population in Northeastern Brazil. Specimens were collected monthly between February 2011 and January 2012 from the Baía do Pontal, Ilhéus, Bahia. We analysed 576 specimens, with females reaching the size at the onset of morphological sexual maturity at a carapace width of 4.7 mm and males at a carapace width of 5.83 mm. Sexual size dimorphism was confirmed, with females exhibiting a broader pleon and males a wider carapace and larger chelipeds. Positive allometry was observed in cheliped growth, with males exhibiting variation among juveniles and adults. Females showed ontogenetic distinctions in pleon width and cheliped dimensions. Our findings reveal that females and males of P. armatus exhibit different energetic investments in the development of secondary sexual characteristics, especially in cheliped growth for males and pleon enlargement for females. These results from a population of P. armatus in Northeastern Brazil contribute to a deeper understanding of reproductive strategies in females and males of the species. [ABSTRACT FROM AUTHOR]

When bivalve aquaculture production relies on natural recruitment, yields may decline due to density‐independent constraints at multiple life stages. These life stage transitions include larval settlement, which is typically variable with rapid losses of newly settled individuals and the additional mortality from predation or abiotic factors (e.g., temperature, desiccation, and physical disturbance) as the bivalves grow. Recruitment monitoring and outplants were used to evaluate the potential limiting factors affecting different life stages in two nonnative clam species, Manila clams, Ruditapes philippinarum, and softshell clams, Mya arenaria in Willapa Bay, Washington, USA. Recruits (250–500 µm) did not differ in cumulative abundance in 2023 relative to prior years of monitoring (five recruitment seasons between 2011 and 2017). Recruits surviving to the end of the summer represented 12% or less of those that had arrived, but still showed spatial patterns consistent with rates of arrival. Manila clams outplanted across an elevation gradient suffered high mortality below mean lower low water regardless of size class (small: 8 mm and large: 20 mm), where native rock crabs (Cancer productus) were abundant. Clam growth declined at higher tidal elevations consistent with inundation time. European green crabs (Carcinus maenas) were relatively abundant at midtidal levels where commercial clam aquaculture typically occurs in the bay and where small clams were particularly reduced without predator protection from mesh. While these data support that green crabs may be reducing survival of 1‐year‐old clams at midintertidal elevations, they also identify earlier bottlenecks to repopulating commercial clam beds, which point out why seeding clams is used to maintain consistent production. Further exploration is needed before green crabs can be singled out as a new limit on clam yields relative to the roles of predation across the size classes of clams in Willapa Bay. [ABSTRACT FROM AUTHOR]

Many coastal ecosystems are impacted by human pressures. Rocky reefs are structurally complex habitats that often support elevated fish abundance and marine biodiversity. In the Baltic Sea, rocky reefs have suffered from extraction for decades, leading to a decrease in hard substrata and complex habitat availability.This study is the first to restore cobble reefs and examine the biological effects.Baited and unbaited underwater video systems (BRUVS and UBRUVS, respectively) were employed across five years to monitor fish communities before reef deployment in 2017 and after reef deployment in 2018 and 2021.Using a before–after control‐impact (BACI) study design with replicates, relative abundances of Atlantic cod (Gadus morhua), herring (Clupeidae sp.), goldsinny wrasse (Ctenolabrus rupestris), two‐spotted goby (Pomatoschistus flavescens), shore crab (Carcinus maenas), and flatfish (Pleuronectiformes spp.) were compared across time and test sites. Comparisons were conducted across 1) restored cobble reefs, 2) natural cobble reefs, and 3) sand‐bottom test sites.This study found positive reef restoration effects revealed consistently by BRUVS and UBRUVS in three species: Atlantic cod, goldsinny wrasse and two‐spotted goby. These findings indicate that A) it is possible to restore cobble reefs and the associated mobile fauna, but also that B) continued marine extraction of cobble degrades complex habitats to the detriment of various marine species.To preserve Atlantic cod, and other sensitive species, we emphasize ecosystem restoration and warn against marine cobble reef extraction in vulnerable areas. Restoration of marine habitats may contribute to achieving the UN sustainable development goal covering life below water. [ABSTRACT FROM AUTHOR]

Mud crabs are common edible crustaceans, which are fished along the coasts of India. Scylla tranquebarica (Fabricius 1798), commonly called green crab is one of the most economically important portunid crab in India. The study was carried out to determine the sex ratio, maturation and spawning, gonadosomatic index, fecundity and egg diameter. Sex ratio of 1 female to 1.3 male gave good results. Size at first maturity was observed at 11 cm carapace width (CW) in males and 10 cm (CW) in females. The highest GSI values in males (6.17) and females (5.12) were observed in the month of October. The maximum number of eggs produced by the females was up to 5 million. The egg diameter was recorded in the range of 0.69 to 0.76 mm. The incubation period was 11-13 days. The hatching success average percentage was recorded as 80%. For the incubation and larval rearing of mud crab, Scylla tranquibarica, the optimum requirement of water temperature and salinity were recorded as 28°C and 30 ppt, respectively. [ABSTRACT FROM AUTHOR]

Simple Summary: Injection of acetic acid into one leg of a crab caused rubbing of that leg and holding the leg off the floor of a tank. Such activities directed towards the site of a noxious stimulus are consistent with the idea of pain. Some crabs also cast off the leg injected with acid. Because that occurred in association with possible pain-related behaviour, it too might be caused by pain. Prior morphine injection caused various behavioural changes, but morphine did not ameliorate the responses to acetic acid. Therefore, morphine does not act as an analgesic, and this agrees with previous work. Nevertheless, the directed behaviour that follows injection into a leg agrees with other studies and provides additional evidence suggesting that these animals experience pain. Noxious chemicals, coupled with morphine treatment, are often used in studies on pain in vertebrates. Here we show that injection of morphine caused several behavioural changes in the crab, Carcinus maenas, including reduced pressing against the sides of the enclosure and more rubbing and picking at the mouth parts and, at least for a short time, more defensive displays. Subsequent injection of acetic acid into one rear leg caused rubbing of the injected leg and the injected leg was held vertically off the ground. These activities directed at or involving the specific leg are consistent with previous observations of directed behaviour following noxious stimuli and are consistent with the idea that decapods experience pain. Further, acetic acid but not injection of water induced autotomy of the injected leg in these animals. Because autotomy is temporally associated with directed behaviour, it is possible that the autotomy is a pain-related response. Acetic acid is clearly a noxious substance when applied to decapods. However, morphine had no effect on the activities associated with acetic acid injection and thus there is no evidence for an analgesic effect. Further, the injection of acetic acid did not interfere with behavioural effects of morphine. The activities directed towards the site of injection are like those observed with injection, or with external application, of various noxious substances and the present study adds to a growing body of knowledge about possible pain in decapods. [ABSTRACT FROM AUTHOR]

We present a case study using trapping data and species accumulation theory to assess the sampling effort needed to detect species that are rare in habitats sampled as part of the management of invasive European green crab Carcinus maenas on the coast of Washington State and Salish Sea shorelines, such as is desired for early detection of invasive species. In response to detections of green crab on the west coast of North America monitoring efforts, including early detection monitoring, have increased. The goal of invasive species early detection monitoring programs is to detect new infestations soon after introduction so that eradication and quarantine measures can be used to control their spread. However, detection of newly introduced invasive species often occurs after populations are large and well established. The ability to detect newly introduced invasive species is affected by sampling procedures, including how much effort is expended. To assess the level of trapping effort needed to detect green crab and other taxa when they are rare, we calculate sample-based rarefaction curves, total species richness, and estimates of sample completeness. We then use these estimates to describe the relationship between sampling effort and detection at two different spatial scales. Our results suggest that high probability early detection of green crabs or other rare taxa in many coastal waterbodies will require significantly more trapping effort than was expended in 2020. Our analyses further suggest that the effort required to provide for early detection was less at the site-specific spatial scale than at the waterbody scale. However, sample completeness at the site-specific spatial scale was negatively correlated with species richness. Current efforts to look for new green crab populations and to manage existing populations provide an opportunity to look for other invasive organisms that may establish in similar habitats. [ABSTRACT FROM AUTHOR]

Predation by invasive species can threaten local ecosystems and economies. The European green crab (Carcinus maenas), one of the most widespread marine invasive species, is an effective predator associated with clam and crab population declines outside of its native range. In the U.S. Pacific Northwest, green crab has recently increased in abundance and expanded its distribution, generating concern for estuarine ecosystems and associated aquaculture production. However, regionally-specific information on the trophic impacts of invasive green crab is very limited. We compared the stomach contents of green crabs collected on clam aquaculture beds versus intertidal sloughs in Willapa Bay, Washington, to provide the first in-depth description of European green crab diet at a particularly crucial time for regional management. We first identified putative prey items using DNA metabarcoding of stomach content samples. We compared diet composition across sites using prey presence/absence and an index of species-specific relative abundance. For eight prey species, we also calibrated metabarcoding data to quantitatively compare DNA abundance between prey taxa, and to describe an 'average' green crab diet at an intertidal slough versus a clam aquaculture bed. From the stomach contents of 61 green crabs, we identified 54 unique taxa belonging to nine phyla. The stomach contents of crabs collected from clam aquaculture beds were significantly different from the stomach contents of crabs collected at intertidal sloughs. Across all sites, arthropods were the most frequently detected prey, with the native hairy shore crab (Hemigrapsus oregonensis) the single most common prey item. Of the eight species calibrated with a quantitative model, two ecologically-important native species–the sand shrimp (Crangon franciscorum) and the Pacific staghorn sculpin (Leptocottus armatus)–had the highest average DNA abundance when detected in a stomach content sample. In addition to providing timely information on green crab diet, our research demonstrates the novel application of a recently developed model for more quantitative DNA metabarcoding. This represents another step in the ongoing evolution of DNA-based diet analysis towards producing the quantitative data necessary for modeling invasive species impacts. [ABSTRACT FROM AUTHOR]

Diatoms are among the most common epibionts and have been recorded on the surfaces of various living substrates, either plants or animals. However, studies on them are still scarce in view of the many substrata available. In this study, epibiotic diatoms living on Callinectes bellicosus were identified for the first time from a subtropical coastal lagoon in Northwest Mexico. We tested the null hypothesis that the diatom flora living on the carapaces of C. bellicosus would not be similar to that recorded for mangrove sediments, its typical habitat. The epibiotic diatoms were brushed off from the carapaces of two specimens, acid-cleaned, mounted in synthetic resin, and identified based on frustule morphology. This way, 106 taxa from 46 genera were recorded, including 25 singletons, and 6 new records for the Mexican northwest region. The best-represented genera were Nitzschia (10 taxa), Mastogloia (9), Diploneis (8), Navicula (7), Amphora (5), Cocconeis (5), Tryblionella (4), and Gyrosigma (4). Species composition included 93% of local taxa, thus refuting the proposed hypothesis and supporting the alternate one. Although the estimated species richness was lower than that in sediments, it deems the green crab carapace a favorable substrate for the growth of benthic diatoms. [ABSTRACT FROM AUTHOR]

Overcoming ecological feedbacks is a major limiting factor reducing the success of many seagrass restoration projects. Negative feedbacks occur when biotic or abiotic conditions of a site are changed sufficiently after the loss of seagrass to prevent its recovery, even after the original stressors are remediated. While negative feedbacks in seagrass restoration are common, there remain limited studies of ways to reduce them and kick‐start the necessary positive feedbacks to promote recovery. We used field and laboratory experiments to investigate key ecological feedbacks in seagrass (Zostera marina) restoration by testing the role of hessian bags and seed burial in reducing seed predation and promoting plant development. We used a double‐hurdle model approach to predict "seagrass emergence success" and "seagrass growth success" across planted field plots. We found that planting seeds in hessian bags and burying them in the sediment improved the likelihood of seeds developing into mature plants. We recorded an average 13‐fold increase in shoot density for seeds planted in buried bags relative to raked furrows. This could be the combined result of reduced predation as well as bags mimicking emergent traits of mature seagrass to withstand physical impacts. We supplement these findings with laboratory evidence that hessian bags provide protection from predation by green shore crabs. Overall, we found a low and variable success rate for seed‐based restoration and indicate other feedbacks in the system beyond those we controlled. However, we show that small methodological changes can help overcome some key feedbacks and improve restoration success. [ABSTRACT FROM AUTHOR]

Decapod crustaceans provide a valuable food source worldwide, both through wild capture and captive rearing. They are also used extensively in scientific research, both as subjects for the investigation of basic biological processes and as model organisms for the detection of environmental changes. There is now an increasing acceptance that decapod crustaceans are sentient, and legislation is being introduced in numerous countries to ensure crustacean welfare when they are harvested or held captive. Moreover, methods for the humane slaughter of these animals are being developed, and of these electrical stunning is a prime candidate. Optimisation of electrical stunning is underway for a range of commercially-exploited or scientifically-important species, and the present study contributes to that process by examining further crab (Carcinus maenas) and lobster (Homarus gammarus) species using a rigorous neurophysiological approach. By recording nerve activity in both the central and peripheral nervous systems, we have found that electrical stunning with a standard commercial instrument arrests nerve activity in both these species at all levels: sensory, motor and central, rendering the animals neurologically insensible. This methodology is the most direct and effective way to establish if insensibility is successfully achieved. However, ultimately the routine monitoring of effective stunning in commercial and laboratory settings will have to depend on simple, yet reliable physiological or behavioural indicators, following their calibration against neurological methods. Monitoring heartbeat is used widely to establish metabolic activity, locomotory performance, agonistic interactions and responses to environmental conditions. We have therefore assessed the potential to use cardiac activity as an indicator for the state of sensibility. We recorded the heartbeat in both C. maenas and H. gammarus before and after electrical stunning, but find that in many cases even though nerve activity has ceased both centrally and peripherally, cardiac activity actually continues (though at a reduced rate) for a substantial time (>1h). The heartbeat is therefore not a reliable indicator of the state of sensibility, making it an unsuitable indicator of effective stunning. Possible reasons for these findings, and ways to validate behavioural measures that may be more appropriate for routinely establishing effective electrical stunning, are discussed. [ABSTRACT FROM AUTHOR]

Simple Summary: Climate change potentially threatens biodiversity, and in a changing environment, it is vitally important that we learn to understand how animals react to the predicted changes. In marine organisms, the sense of smell governs almost all essential behaviours animals exhibit, from finding food and detecting a predator to finding a mating partner. Interpreting animal behaviour when exposed to odour is a complex task, as many factors from seasonality to individuality, fitness, social status, and even weather and water chemistry influence an individual's response. Here, we examine the impacts of reducing seawater pH levels predicted for the end of the century upon decision-making in male shore crabs when exposed to the female reproductive odour, the female sex pheromone. There is a significant alteration in the responsiveness of male crabs, with large, more sexually active males taking significantly less time to detect and react to females but then showing less sexual mating activity once reaching the female odour. This disruption of olfactory communication can potentially impact the mating and reproductive success of this globally distributed species, showing that even coastal crustaceans that are known to be hardy and able to survive substantial stressors are potentially at risk from altered seawater chemistry associated with climate change. The effects of climate change are becoming more apparent, predominantly concerning the impacts of ocean acidification on calcifying species. Many marine organisms rely on chemical signals for processes such as foraging for food, predator avoidance, or locating mates. The process of how chemical cues in marine invertebrates function, and how this sensory mode is affected by pH levels, is less researched. We tested the impact of reduced pH (7.6), simulating end-of-the-century predicted average ocean pH, against current oceanic pH conditions (8.2), on the behavioural response of male shore crabs Carcinus maenas to the female sex pheromone bouquet consisting of Uridine–diphosphate (UDP) and Uridine–triphosphate (UTP). While in current pH conditions (8.2), there was a significant increase in sexual interactions in the presence of female pheromone, males showed reduced sexual behaviours at pH 7.6. The crab weight–pH relationship, in which larger individuals respond more intensely sexually in normal pH (8.2), is reversed for both the initial detection and time to locate the cue. These results indicate that lowered pH alters chemical signalling in C. maenas also outside the peak reproductive season, which may need to be taken into account when considering the future management of this globally invasive species. [ABSTRACT FROM AUTHOR]

Invasive species are known to alter the progress of ecological restoration, but effects of invasive consumers, and particularly those that can act through both trophic and physical disturbance mechanisms, remain poorly understood. Due to its impacts on vegetation and ability to alter marsh food webs, we predicted that a non-native crab, Carcinus maenas (European green crab), would negatively affect restoration plantings of a native cordgrass, Spartina foliosa 1 (California cordgrass), in San Francisco (SF) Bay, in contrast with neutral or positive impacts predicted for a native crab, Hemigrapsus oregonensis (yellow shore crab). We implemented an experiment in SF Bay using caged plots of planted S. foliosa , to which we added or did not add crabs. We compared responses among these treatments, cageless, and partially-caged controls. Carcinus maenas treatments had the greatest reduction in S. foliosa stem density from June through August, and the lowest stem density in August relative to all other treatments. Hemigrapsus oregonensis effects were similar to controls. Both crabs reduced small invertebrate abundance by ~50% and led to shifts in community composition relative to controls. Changes to the invertebrate community and subtle shifts in soil conditions may contribute to the apparent negative impact of C. maenas. Crab trapping revealed more C. maenas in areas with Spartina in SF Bay, suggesting it uses Spartina as a refuge and that these effects are especially relevant to restoration activities. These results add to our developing understanding that invasive consumers can affect the path and pace of restoration and thus warrant increased attention in restoration planning and management. [ABSTRACT FROM AUTHOR]

Environments contain various forms of noise that can interfere with the ability of animal sensory systems to perceive information. One ubiquitous type of visual noise in shallow aquatic habitats is caustic flicker (or caustics), consisting of dynamically moving light patterns caused by the refraction of light when passing through the water's rippling surface. While some teleost fish avoid environments with caustic noise (where their prey can be more difficult to detect), it remains untested whether caustics affect the habitat selection of invertebrates. In the present study, we ask whether three invertebrate species, the shore crab Carcinus maenas, the brown shrimp Crangon crangon, and the common cuttlefish Sepia officinalis, prefer or avoid associating with environments with caustic noise, and whether caustics affect their behavioural activity and habitat exploration. To do this, we exposed the three species in binary choice experiments to different simulated caustic noise levels varying in their temporal (speed) and spatial (definition) components. Neither of the three tested invertebrate species spent more or less time in environments with higher caustic noise levels. While we also found no evidence that caustics affected the behavioural activity and exploration of Ca. maenas and S. officinalis, the brown shrimp Cr. crangon reduced its activity with increasing spatial caustic noise. However, all obtained effect sizes in this study were small, suggesting that caustic noise only minimally affects invertebrate behaviour. Overall, our results show that, unlike in teleost fish, caustics have limited influence on the habitat selection, exploration, and activity of crustaceans and cephalopods. [ABSTRACT FROM AUTHOR]

Simple Summary: The idea that invertebrates feel pain is often dismissed because of claims that their responses to noxious stimuli are simply reflexes. Reflexes do not require higher-order processing, but that is required for pain experience. One way to test this claim is to ask if animals only respond to the noxious stimulus or if that response can be influenced by other motivations. Here, we report that shore crabs that enter a dark shelter from a light area and receive a shock are subsequently less likely to use that shelter if the light level is low and the shock level high. They trade their requirement to avoid bright light for the avoidance of the noxious shock. They learn to avoid the shelter and show signs of anxiety when deciding to enter the shelter to escape the light. These observations demonstrate that the responses to shock are not reflexes but are decisions that should improve the outcome better than a reflex alone. This balancing of needs is a key expectation of pain, and the results are consistent with the idea that crabs feel pain. The suggestion that decapod crustaceans might experience pain has been dismissed by some authors who claim decapods only respond to noxious stimuli by nociceptive reflexes. Because reflexes do not require complex neuronal processing, but pain does, demonstrating reflex responses to noxious stimuli would not support the case for pain. Here, we report an experiment in which shore crabs are repeatedly placed in a light area (20 trials), but the animals can avoid the light by moving to a dark shelter. However, some crabs received an electric shock of 6 or 12 volts each time they entered the shelter. Those receiving either level of shock swiftly reduced their use of shelters and remained in the light. However, the magnitude of shelter avoidance was influenced by the brightness of the arena and the intensity of the shock. Shelter use was subsequently reduced to a greater extent if the shock level was high and the light intensity low. That is, crabs traded their avoidance of shock for their avoidance of bright light. Further, these animals showed avoidance learning and demonstrated activities suggesting anxiety, such as contact with the tank wall in the light area and increased latency to enter shelters when making the decision to enter the shelter if they had received shock in earlier trials. These results fulfil three key behavioural criteria for pain and, thus, are consistent with the idea that decapods can experience pain. [ABSTRACT FROM AUTHOR]

Aim: To determine whether the crustacean Rh1 protein functions as a dual CO2/ammonia transporter and investigate its role in branchial ammonia excretion and acid–base regulation. Methods: Sequence analysis of decapod Rh1 proteins was used to determine the conservation of amino acid residues putatively involved in ammonia transport and CO2 binding in human and bacterial Rh proteins. Using the Carcinus maenas Rh1 protein (CmRh1) as a representative of decapod Rh1 proteins, we test the ammonia and CO2 transport capabilities of CmRh1 through heterologous expression in yeast and Xenopus oocytes coupled with site‐directed mutagenesis. Quantitative PCR was used to assess the distribution of CmRh1 mRNA in various tissues. Western blotting was used to assess CmRh1 protein expression changes in response to high environmental ammonia and CO2. Further, immunohistochemistry was used to assess sub‐cellular localization of CmRh1 and a membrane‐bound carbonic anhydrase (CmCAg). Results: Sequence analysis of decapod Rh proteins revealed high conservation of several amino acid residues putatively involved in conducting ammonia transport and CO2 binding. Expression of CmRh1 in Xenopus oocytes enhanced both ammonia and CO2 transport which was nullified in CmRh1 D180N mutant oocytes. Transport of the ammonia analog methylamine by CmRh1 is dependent on both ionized and un‐ionized ammonia/methylamine species. CmRh1 was co‐localized with CmCAg to the apical membrane of the crustacean gill and only experienced decreased protein expression in the anterior gills when exposed to high environmental ammonia. Conclusion: CmRh1 is the first identified apical transporter‐mediated route for ammonia and CO2 excretion in the crustacean gill. Our findings shed further light on the potential universality of dual ammonia and CO2 transport capacity of Rhesus glycoproteins in both vertebrates and invertebrates. [ABSTRACT FROM AUTHOR]

Understanding the density-dependent impacts of an invasive predator is integral for predicting potential consequences for prey populations. Functional response experiments are used to assess the rate of prey consumption and a predator's ability to search for and consume prey at different resource densities. However, results can be highly context-dependent, limiting their extrapolation to natural ecosystems. Here, we examined how simulated habitat complexity, through the addition of substrate in which prey can escape predation, affects the functional response of invasive European green crabs (Carcinus maenas) foraging on two different bivalve species. Green crabs feeding on varnish clams (Nuttallia obscurata) shifted from a Type II hyperbolic functional response in the absence of substrate to density-independent consumption when prey could bury. Green crabs ate few Japanese littleneck clams (Venerupis philippinarum) under all densities, such that no functional response curve of any type could be produced and their total consumption was always density independent. However, the probability of at least one Japanese littleneck clam being consumed increased significantly with initial clam density and crab claw size across all treatments. At mean crab claw size and compared to trials without substrate, the proportion of varnish clams consumed were 4.2 times smaller when substrate was present, but substrate had a negligible effect (1.2 times) on Japanese littlenecks. The proportion of varnish clams consumed increased with crab claw size and were higher across both substrate conditions than the proportion of Japanese littlenecks consumed; however, the proportion of Japanese littleneck clams consumed increased faster with claw size than that of varnish clams. Our results suggest that including environmental features and variation in prey species can influence the density-dependent foraging described by functional response experiments. Incorporating replicable features of the natural environment into functional response experiments is imperative to make more accurate predictions about the impact of invasive predators on prey populations. [ABSTRACT FROM AUTHOR]

Invasive predators can cause substantial evolutionary change in native prey populations. Although invasions by predators typically occur over large scales, their distributions are usually characterized by substantial spatiotemporal heterogeneity that can lead to patchiness in the response of native prey species. Our ability to understand how local variation shapes patterns of inducible defense expression has thus far been limited by insufficient replication of populations within regions. Here, we examined local and regional variation in the inducible defenses of 12 native marine snail (Littorina obtusata) populations within two geographic regions in the Gulf of Maine that are characterized by vastly different contact histories with the invasive predatory green crab (Carcinus maenas). When exposed in the field to waterborne risk cues from the green crab for 90 days, snails expressed plastic increases in shell thickness that reduced their vulnerability to this shell‐crushing predator. Despite significant differences in contact history with this invasive predator, snail populations from both regions produced similar levels of shell thickness and shell thickness plasticity in response to risk cues. Such phenotypic similarity emerged even though there were substantial geographic differences in the shell thickness of juvenile snails at the beginning of the experiment, and we suggest that it may reflect the effects of warming ocean temperatures and countergradient variation. Consistent with plasticity theory, a trend in our results suggests that southern snail populations, which have a longer contact history with the green crab, paid less in the form of reduced tissue mass for thicker shells than northern populations. [ABSTRACT FROM AUTHOR]

Caffeine is one of the most consumed substances by humans through foodstuffs (coffee, tea, drugs, etc.). Its human consumption releases a high quantity of caffeine into the hydrological network. Thus, caffeine is now considered an emergent pollutant sometimes found at high concentrations in oceans and seas. Surprisingly, little research has been conducted on the molecular responses induced by caffeine in marine organisms. We studied, in laboratory conditions, six phylogenetically distant species that perform distinct ecological functions (Actinia equina and Aulactinia verrucosa (cnidarians, predator), Littorina littorea (gastropod, grazer), Magallana gigas (bivalve, filter-feeder), and Carcinus maenas and Pachygrapsus marmoratus (crabs, predator and scavenger)) subjected to caffeine exposure. The antioxidant responses (catalase, CAT; glutathione peroxidase, GPx; superoxide dismutase, SOD), lipid peroxidation (MDA), and the acetylcholinesterase (AChE) activity were estimated when the organisms were exposed to environmental caffeine concentrations (5 μg/L (low), 10 μg/L (high)) over 14 days. Differential levels of responses and caffeine effects were noted in the marine invertebrates, probably in relation to their capacity to metabolization the pollutant. Surprisingly, the filter feeder (M. gigas, oyster) did not show enzymatic responses or lipid peroxidation for the two caffeine concentrations tested. The marine gastropod (grazer) appeared to be more impacted by caffeine, with an increase in activities for all antioxidative enzymes (CAT, GPx, SOD). In parallel, the two cnidarians and two crabs were less affected by the caffeine contaminations. However, caffeine was revealed as a neurotoxic agent to all species studied, inducing high inhibition of AChE activity. This study provides new insights into the sublethal impacts of caffeine at environmentally relevant concentrations in marine invertebrates. [ABSTRACT FROM AUTHOR]

Artificial light at night (ALAN) disrupts biological processes across taxa and at all levels of organisation. Despite growing interest in this globally pervasive sensory pollutant, its impact on colour-guided processes remains largely unexplored. This is especially concerning given the rapid transition in recent years away from narrow-spectrum lighting and towards broad-spectrum options such as white LEDs, which are rich in the short wavelengths of light to which many taxa are particularly sensitive. Camouflage is particularly likely to be disrupted by broader spectra of ALAN due to changes in conspicuousness in background matching prey, which may alter prey recognition in visually guided predators. We simulated natural intensities of moonlight with and without ALAN, using both broad-spectrum ('white') ALAN and ALAN filtered to remove the characteristic short (blue) wavelength peak of broad-spectrum LEDs to test whether filtering might mitigate their effects. We tested how exposure to these light treatments impacted predator-prey interactions, using the intertidal crab Carcinus maenas and contrasting colour morphs of the colour-polymorphic snail Littorina obtusata as a model system. Exposure to broad-spectrum ALAN reduced overall predation and reversed the pattern of colour-based prey selection observed under control conditions. Snails were 55 % less likely to be attacked under broad-spectrum ALAN than in control conditions, with likelihood decreasing over 70 % for yellow snails. Yellow snails were over 26 % more likely to be attacked than brown ones under control conditions, but brown snails were over 40 % more likely to be attacked than yellow ones under broad-spectrum ALAN. Exposure to filtered ALAN removed any significant colour-based difference in prey recognition. Our results demonstrate that spectral composition is a crucial aspect of ALAN as a sensory pollutant, capable of instigating profound changes in predator-prey interactions that could drive changes in population demography and increase morphological homogeneity in species that depend on colour polymorphism for camouflage. [ABSTRACT FROM AUTHOR]

Prey respond to predation risk by altering their morphology, physiology, and behavior, responses that may come at a cost to prey foraging and growth. However, their perception of risk may depend upon the environmental context in which the interaction occurs. Here, we examined how food availability influenced prey's responses to a nonlethal but free-ranging predator. We used an experimental mesocosm set-up of an intertidal system of green crab (Carcinus maenas) predators and dogwhelk snail (Nucella lapillus) prey, with blue mussels as the basal resource. We measured individual Nucella risk-aversion behavior (summed value of their habitat use) and their growth throughout the 28-day experiment. We found that when Nucella were exposed to predation risk, they had greater risk-aversion behavior when food was available as compared to when food was not. We also found that risk-aversion behavior increased over time in all treatments but that individuals exposed to predation risk with food always had greater risk-aversion behavior. Nucella had significantly more growth when provided with food as compared to without. In treatments with food, snails exposed to predation risk had significantly reduced growth compared to those not exposed to risk. In treatments without food, predation risk had no effect on growth. Our results support the hypothesis that greater resource availability significantly increases individual risk responses and the costs of risk avoidance, thus food magnifies risk-induced non-consumptive effects. They provide insights into context-based predation risk effects and how individuals may prioritize safety versus foraging depending upon perceived risk, food availability, and the costs of responding. [ABSTRACT FROM AUTHOR]

Introduction: At the cellular level, acute temperature changes alter ionic conductances, ion channel kinetics, and the activity of entire neuronal circuits. This can result in severe consequences for neural function, animal behavior and survival. In poikilothermic animals, and particularly in aquatic species whose core temperature equals the surrounding water temperature, neurons experience rather rapid and wide-ranging temperature fluctuations. Recent work on pattern generating neural circuits in the crustacean stomatogastric nervous system have demonstrated that neuronal circuits can exhibit an intrinsic robustness to temperature fluctuations. However, considering the increased warming of the oceans and recurring heatwaves due to climate change, the question arises whether this intrinsic robustness can acclimate to changing environmental conditions, and whether it differs between species and ocean habitats. Methods: We address these questions using the pyloric pattern generating circuits in the stomatogastric nervous system of two crab species, Hemigrapsus sanguineus and Carcinus maenas that have seen a worldwide expansion in recent decades. Results and discussion: Consistent with their history as invasive species, we find that pyloric activity showed a broad temperature robustness (>30°C). Moreover, the temperature-robust range was dependent on habitat temperature in both species. Warm-acclimating animals shifted the critical temperature at which circuit activity breaks down to higher temperatures. This came at the cost of robustness against cold stimuli in H. sanguineus, but not in C. maenas. Comparing the temperature responses of C. maenas from a cold latitude (the North Sea) to those from a warm latitude (Spain) demonstrated that similar shifts in robustness occurred in natural environments. Our results thus demonstrate that neuronal temperature robustness correlates with, and responds to, environmental temperature conditions, potentially preparing animals for changing ecological conditions and shifting habitats. [ABSTRACT FROM AUTHOR]

Understanding the relationship between environmental temperature and the biological traits of organisms is fundamental to inferring the potential impacts of climate change. In the case of marine poikilotherm species, seawater temperature is one of the main driving forces of biological processes, with consequences at higher levels of organization such as population and ecosystem. In this study, we analysed differences in maximum carapace width (CWmax), size at maturation, relative size at maturation, and duration of the reproductive season for the green crab (Carcinus maenas) along a temperature gradient. An extensive review of bibliographic data was performed on studies published between 1962 and 2020, gathering C. maenas data from 55 different populations, spread over 20 degrees of latitude and 14.2 °C of sea surface temperature (SST). In addition, green crab data were collected at five different lagoons and estuaries along the continental Portuguese coast. The relationship between average SST and CWmax, age of maturation, reduction of size at maturation, and duration of egg bearing was analysed to understand the role of SST in driving variation in these C. maenas characteristics across a latitudinal gradient. There was a significant relationship between SST and CWmax for males and SST and CW of females at maturation, respectively. The results extrapolate for each local projected temperature increase caused by climate change and suggest an effect on the morphometric and reproductive traits of C. maenas across regions. These changes comprise an overall reduction in C. maenas body size, an enlargement of the reproductive season, a shortening in the duration of larval developmental time, and a decrease in the relative size of crabs at maturation. Secondary consequences on the fecundity and connectivity of populations are discussed. [ABSTRACT FROM AUTHOR]

Crustaceans' endocrinology is a vastly understudied area of research. The major focus of the studies on this topic to date has been on the molting cycle (and in particular, the role of crustacean hyperglycemic hormone (CHH)), as well as the role of other hormones in facilitating physiological phenotypic adjustments to salinity changes. Additionally, while many recent studies have been conducted on the acclimation and adaptation capacity of crustaceans to a changing environment, only few have investigated internal hormonal balance especially with respect to an endocrine response to environmental challenges. Consequently, our study aimed to identify and characterize endocrine components of acid–base regulation in the European green crab, Carcinus maenas. We show that both the biogenic amine octopamine (OCT) and the CHH are regulatory components of branchial acid–base regulation. While OCT suppressed branchial proton excretion, CHH seemed to promote it. Both hormones were also capable of enhancing branchial ammonia excretion. Furthermore, mRNA abundance for branchial receptors (OCT-R), or G-protein receptor activated soluble guanylate cyclase (sGC1b), are affected by environmental change such as elevated pCO2 (hypercapnia) and high environmental ammonia (HEA). Our findings support a role for both OCT and CHH in the general maintenance of steady-state acid–base maintenance in the gill, as well as regulating the acid–base response to environmental challenges that C. maenas encounters on a regular basis in the habitats it dwells in and more so in the future ocean. [ABSTRACT FROM AUTHOR]

Noxious chemicals, coupled with morphine treatment, are often used in studies on pain in vertebrates. Here we show that injection of morphine caused several behavioural changes in the crab, Carcinus maenas, including reduced pressing against the sides of the enclosure and more rubbing and picking at the mouth parts and, at least for a short time, more defensive displays. Subsequent injection of acetic acid into one rear leg caused rubbing of the injected leg and the injected leg was held vertically off the ground. These activities directed at or involving the specific leg are consistent with previous observations of directed behaviour following noxious stimuli and are consistent with the idea that decapods experience pain. Further, acetic acid but not injection of water induced autotomy of the injected leg in these animals. Because autotomy is temporally associated with directed behaviour, it is possible that the autotomy is a pain-related response. Acetic acid is clearly a noxious substance when applied to decapods. However, morphine had no effect on the activities associated with acetic acid injection and thus there is no evidence for an analgesic effect. Further, the injection of acetic acid did not interfere with behavioural effects of morphine. The activities directed towards the site of injection are like those observed with injection, or with external application, of various noxious substances and the present study adds to a growing body of knowledge about possible pain in decapods.

Camouflage plays a significant role in preventing and facilitating predation. A common method used by many species to avoid detection is to match aspects of the visual background. Behaviour can constitute a valuable component of camouflage by enabling animals to choose appropriate substrates, yet how widespread this is remains relatively underexplored. Through a series of substrate choice experiments we tested whether the highly phenotypically diverse common shore crab shows substrate preferences, and whether preferences reflect choices that actively improve individual camouflage. Using image analysis, we compared brightness and colour metrics of crabs to their chosen versus alternative substrates. Crabs tended to choose substrates with a brightness that better matched their own appearance. However, choices depended on the exact backgrounds offered, for example with crabs preferring backgrounds resembling native rock pool colour patterns over those resembling mudflats, but showing little difference in choice between red and green substrates. The results help explain observations that shore crabs and other animals show phenotype–environment associations at a microscale and demonstrate how individuals can maintain camouflage in highly variable visual environments. Our study shows that substrate preferences can be a key route to enabling camouflage in a broad spectrum of species. • Camouflage is an essential strategy to avoid predation. • Many animals may use behaviour to choose substrates that match their appearance. • Shore crabs show substrate preferences for camouflage depending on their coloration. • Behavioural background matching likely plays a key role in facilitating camouflage. [ABSTRACT FROM AUTHOR]

Seagrass beds support diverse macrofaunal communities, and collectively they influence carbon and nutrient cycles; however, we know little on how seagrass disturbance alters this relationship. In Newfoundland, Canada, the invasive European green crab Carcinus maenas threatens the seagrass Zostera marina by snipping and uprooting seagrasses while foraging and burrowing. In order to understand the effects of seagrass disturbance on macrofaunal diversity and ecosystem functioning within sediments, we experimentally uprooted small patches of seagrass and compared rates of oxygen and nutrient fluxes from sediment cores from uprooted (disturbed) patches, seagrasses, and unvegetated sediments nearby. In parallel, we assessed macrofaunal biodiversity (taxonomic and functional) and sedimentary (granulometric properties and organic matter content/freshness) variables in all three of these treatments over a three‐month period. As expected, macrofaunal abundance, species richness and functional richness declined significantly initially in disturbed cores, although this decrease had little effect on benthic flux rates. Over 3 months, macrofaunal colonization of the disturbed sediments resulted in abundances similar to the natural seagrass and unvegetated treatments. We also observed a change in nutrient flux rates that we attribute to seasonal shifts in regeneration pathways rather than macrofaunal community recovery, suggesting a lesser role for macrofaunal diversity in carbon and nutrient cycling in dynamic nearshore habitats than in deeper water. Our results demonstrate the impacts of green crab‐mediated seagrass disturbance on macrofaunal abundance and community structure while highlighting their potential capacity for rapid stabilization, and emphasize the strength of large‐scale seasonal environmental changes on ecosystem processes. [ABSTRACT FROM AUTHOR]

The suggestion that decapod crustaceans might experience pain has been dismissed by some authors who claim decapods only respond to noxious stimuli by nociceptive reflexes. Because reflexes do not require complex neuronal processing, but pain does, demonstrating reflex responses to noxious stimuli would not support the case for pain. Here, we report an experiment in which shore crabs are repeatedly placed in a light area (20 trials), but the animals can avoid the light by moving to a dark shelter. However, some crabs received an electric shock of 6 or 12 volts each time they entered the shelter. Those receiving either level of shock swiftly reduced their use of shelters and remained in the light. However, the magnitude of shelter avoidance was influenced by the brightness of the arena and the intensity of the shock. Shelter use was subsequently reduced to a greater extent if the shock level was high and the light intensity low. That is, crabs traded their avoidance of shock for their avoidance of bright light. Further, these animals showed avoidance learning and demonstrated activities suggesting anxiety, such as contact with the tank wall in the light area and increased latency to enter shelters when making the decision to enter the shelter if they had received shock in earlier trials. These results fulfil three key behavioural criteria for pain and, thus, are consistent with the idea that decapods can experience pain.

Predicting the impacts of predatory invasive species is important for prioritising conservation interventions. Functional response experiments, which examine consumption by predators in relation to prey density, are a useful way to assess the potential strength of novel predator-prey relationships. However, such experiments are often conducted without consideration of sex or only with males to reduce invasion risk. Here, we compared the functional responses of male and female European green crabs (Carcinus maenas), a global invader, feeding on varnish clams (Nuttallia obscurata) to test whether the two sexes have similar potential for impact. We also examined potential correlates of predation behaviour by measuring sex-specific movement and prey choice. Both sexes displayed a Type II hyperbolic functional response, which can destabilise prey populations at low prey densities. However, males and females exhibited some differences in foraging behaviour. Female green crabs had slightly lower attack rates, which were not linked to sex differences in movement, and slightly longer handling times, which were not linked to sex differences in prey choice. These small, non-significant differences nevertheless translated into significantly greater functional response ratios, which are used to predict the ecological impact of invasive species, for males than females. There was no difference in the proportion of clams consumed between males and females with similar crusher claw heights, but females have smaller crusher claws on average, hence they consumed a smaller proportion of clams. Repeated surveys of four populations of European green crabs established in British Columbia, Canada, showed that sex ratio is highly variable. Taken together, these results and population-level modelling suggest that trying to evaluate the potential impact of European green crabs on clam populations by sampling only males could result in overestimation, even in populations that have male-biased sex-ratios. Consumer sex might generally be an important feature to consider when using functional response experiments to forecast the impact of new invasive species, especially those with marked sexual dimorphism that affect foraging. [ABSTRACT FROM AUTHOR]

Baited remote underwater video station (BRUVS) investigations of benthic scavenging by fish and invertebrates were conducted in an Irish sea lough. Mackerel (Scomber scombrus) baits were deployed under natural light during the day and under dim red light at night. Ethograms for feeding mechanisms and agonistic behaviours were established for four abundant scavengers (two crabs: the harbour crab Liocarcinus depurator, and the European green crab Carcinus maenas; two fish: the shanny Lipophrys pholis, and the small-spotted catshark Scyliorhinus canicula). Crabs' feeding mechanisms were similar, with differences reflecting their morphologies. Feeding bouts lasted minutes/tens of minutes. Intraspecific agonistic responses were mild and did not result in mutilation or mortality. Feeding mechanisms on macerated baits focussed on 'chewing' (combined use of chelipeds and mouthparts to feed continuously); agonistic behaviour was reduced, especially at night when balls of crabs showed 'cooperative feeding'. Fish feeding bouts lasted for a few seconds in all cases. Shannies showed anticipatory agonistic behaviour (bait 'guarding' and 'patrolling' by large shannies) before bait maceration. Catsharks exhibited no intraspecific agonistic behaviour but removed large bait morsels by 'biting', 'chewing' and 'spinning'. The common prawns Palaemon serratus only scavenged at night and were invisible to other scavengers; they showed no agonistic behaviours. Kleptoparasitism amongst the scavenger guild was common but intra-community predation was extremely rare. Phoretic feeding on bait scraps by red-speckled anemones (Anthopleura ballii) attached to the carapaces of the edible crab Cancer pagurus was observed. [ABSTRACT FROM AUTHOR]

Noisy human activities at sea are changing the acoustic environment, which has been shown to affect marine mammals and fishes. Invertebrates, such as bivalves, have so far received limited attention despite their important role in the marine ecosystem. Several studies have examined the impact of sound on anti-predator behavior using simulated predators, but studies using live predators are scarce. In the current study, we examined the separate and combined effects of boat sound playback and predator cues of shore crabs (Carcinus maenas) on the behavior of mussels (Mytilus spp.). We examined the behavior of the mussels using a valve gape monitor and scored the behavior from the crabs in one of two types of predator test conditions from video footage to control for effects from potential, sound-induced variation in crab behavior. We found that mussels closed their valve gape during boat noise and with a crab in their tank, but also that the stimulus combination did not add up to an even smaller valve gape. The sound treatment did not affect the stimulus crabs, but the behavior of the crabs did affect the valve gape of the mussels. Future research is needed to examine whether these results stand in situ and whether valve closure due to sound has fitness consequences for mussels. The effects on the well-being of individual mussels from anthropogenic noise may be relevant for population dynamics in the context of pressure from other stressors, their role as an ecosystem engineer, and in the context of aquaculture. [ABSTRACT FROM AUTHOR]

Non-native species can have profound implications on the survival of native ones. This is especially true for some invasive crabs, such as the green crab Carcinus maenas, a native species to the Northern Hemisphere that has been introduced into southern Argentina, from where it could expand through Argentina, Chile, and the Antarctic Peninsula. Hence, there is interest in forecasting changes in C. maenas habitat suitability through time to predict if potential future invasions might occur. Here, by using a Species Distribution Model (SDM) approach, we estimated the habitat suitability for C. maenas along southern South America and the Antarctic Peninsula under two future climate-change scenarios. Our results reveal that under current conditions, habitat suitability for C. maenas along the Antarctic Peninsula is null and very restricted in Argentina and Chile. Habitat suitability along the Antarctic Peninsula remained null in the short-term (30 years) and long-term future (80 years), despite the climate-change scenario considered. Surprisingly, when considering future conditions, habitat suitability along the coast of Argentina and Chile decreased and became nil for some currently occupied locations. Thus, the SDM results suggest that climate change could have a negative effect on the habitat suitability of C. maenas leading to potential local extinctions. [ABSTRACT FROM AUTHOR]

Marine invertebrates with biphasic life cycles feature life history transitions that coincide with habitat changes from benthic adults to planktonic embryos and larvae, then a return to the benthos as a juvenile at metamorphosis. The metamorphic transition exposes animals to a new suite of benthic predators, and high mortality often occurs in the hours and days following settlement. Juvenile invertebrates may produce phenotypically plastic morphological defenses when predator cues are detected. However, time lags inherent to phenotypic plasticity may delay the production of defenses until after the period of highest vulnerability. It should, therefore, be beneficial for planktonic larvae approaching settlement to detect waterborne cues from benthic predators and produce juvenile phenotypes appropriate for postmetamorphic survival. Echinoderms are useful models for testing transhabitat and trans–life history stage phenotypic plasticity because many species have larvae that construct their juvenile phenotype while still in the water column. In this study, we tested whether planktonic echinoderm larvae exposed to cues from benthic predators modified their juvenile phenotypes at settlement. Green urchin (Strongylocentrotus droebachiensis) and Pacific sand dollar (Dendraster excentricus) larvae were exposed to predatory green crab (Carcinus maenus) or red rock crab (Cancer productus) cues, respectively, from their early-stage juvenile rudiment formation through settlement. Green urchin larvae exposed to predator cues settled with significantly more juvenile spines compared to unexposed controls. Sand dollars exhibited earlier settlement, larger disk area, fewer spines, and shorter spines when exposed to benthic predator cues. Sand dollar larvae were also exposed to cues from planktonic crab larvae and in response settled sooner and larger, with even fewer and shorter spines than those exposed to benthic predator cues. These results suggest that echinoderm larvae alter their juvenile phenotype in response to predator cues, but the response varies between species, and responses to planktonic threats may be prioritized over benthic ones. [ABSTRACT FROM AUTHOR]

The orphan transporter hippocampus-abundant transcript 1 (Hiat1) was first identified in the mammalian brain. Its specific substrate specificity, however, has not been investigated to date. Here, we identified and analyzed Hiat1 in a crustacean, the green crab Carcinus maenas. Our phylogenetic analysis showed that Hiat1 protein is conserved at a considerable level between mammals and this invertebrate (ca. 78% identical and conserved amino acids). Functional expression of Carcinus maenas Hiat1 in Xenopus laevis oocytes demonstrated the capability to transport ammonia (likely NH4+) in a sodium-dependent manner. Furthermore, applying quantitative polymerase chain reaction, our results indicated a physiological role for Carcinus maenas Hiat1 in ammonia homeostasis, as mRNA abundance increased in posterior gills in response to elevated circulating hemolymph ammonia upon exposure to high environmental ammonia. Its ubiquitous mRNA expression pattern also suggests an essential role in general cellular detoxification of ammonia. Overall, our results introduce a new ubiquitously expressed ammonia transporter, consequently demanding revision of our understanding of ammonia handling in key model systems from mammalian kidneys to crustacean and fish gills. [ABSTRACT FROM AUTHOR]

The experiment was to evaluate the effect of defatted black soldier fly larvae meal on nutritional quality of Scyla paramamosain. A total of 480 healthy green crab seedlings with neat size and an average initial weight of 5.2 g were randomly divided into 12 cement ponds (2 m×1.2 m×1.5 m) and divided into four groups, with three replicates in each group and 40 Scyla paramamosain seedlings in each replicate. The crabs in C group (control group) were fed with basal diet, and 25%, 50% and 75% fish meal in basal diet were replaced by protein such as defatted black horse fly meal in H25 group, H50 group and H75 group, respectively, the four diets were equal in nitrogen and energy. The experiment lasted for 4 w. The results showed that compared with group C, the body length, body width and body weight of crabs in H25 group and H50 group were significantly increased (P<0.05), the body height of crabs in experimental groups was significantly increased (P<0.05), and the body fatness of crabs in H25 group and H75 group was significantly increased (P<0.05). Compared with C group, cysteine content of crab body in H75 group was significantly reduced (P<0.05). Compared with C group, the content of PUFA and PUFA (n-3) in crab body in H75 group were significantly decreased (P<0.05). The experiment indicates that when 25%~50% fish meal is substituted for the diet, the growth effect of green crab is the best, the nutrition quality is better. [ABSTRACT FROM AUTHOR]

Predation risk effects are impacts on prey caused by predators that do not include consumption. These can include changes in prey behaviour, physiology, and morphology (i.e. risk‐induced trait responses), which can have consequences to individual fitness and population dynamics (i.e. non‐consumptive effects). While these risk‐induced trait responses (RITRs) can lower individual fitness as compared to prey not exposed to risk, they are assumed to increase fitness in the presence of predators. While much work has been built upon this assumption, most evidence occurs in consumptive experiments where the trait values of consumed prey are unknown. We have little evidence showing individuals with a greater magnitude of RITR have greater survival.Here, we tested the hypothesis that RITRs increase survival in the presence of predators, but come at a cost to growth. We tested this hypothesis using Nucella lapillus as prey and Carcinus maenas as a predator and including mussels as a basal resource in a two‐phase mesocosm experimental set‐up. In phase 1, Nucella were placed into either a control or risk treatment (exposure to non‐lethal Carcinus) for 28 days and their behaviour and growth measured. In phase 2, a lethal Carcinus was added to all mesocosms (non‐lethal crabs were removed), and survival was recorded for 15 days.At the treatment (group) level, we found that Nucella exposed to predation risk in phase 1 had significantly greater risk aversion behaviour (summed score of risky vs. safe behaviour) and significantly lower growth. In phase 2, we found that Nucella exposed to predation risk had greater survival.At the individual level (regardless of treatment), we found that Nucella with greater risk aversion scores in phase 1 had significantly higher survival in phase 2 when exposed to a lethal predator, but this came at a cost to their growth.This study provides some of the first empirical evidence, at both the group and individual level, testing a long‐held assumption that predation risk‐induced behavioural responses increase survival in the face of direct predation, but that these responses come at a cost to the prey. These results add to our growing understanding of the benefits of RITRs to individual fitness and non‐consumptive effects generally. [ABSTRACT FROM AUTHOR]

At low tide, the green crab, which is capable of breathing air, may leave the water and walk on the foreshore, carrying branchial chamber fluid (BCF). N‐waste metabolism was examined in crabs at rest in seawater (32 ppt, 13°C), and during 18‐h recovery in seawater after 1 h of exhaustive exercise (0.25 BL s−1) on a treadmill in air (20°C–23°C), or 1 h of quiet emersion in air. Measurements were made in parallel to O2 consumption (ṀO2), acid‐base, cardio‐respiratory, and ion data reported previously. At rest, the ammonia‐N excretion rate (ṀAmm = 44 µmol‐N kg−1 h−1) and ammonia quotient (AQ; ṀAmm/ṀO2 = 0.088) were low for a carnivore. Immediately after exercise and return to seawater, ṀAmm increased by 65‐fold above control rates. After emersion alone and return to seawater, ṀAmm increased by 17‐fold. These ammonia‐N bursts were greater, but transient relative to longer‐lasting elevations in ṀO2, resulting in temporal disturbances of AQ. Intermittent excretion of urea‐N and urate‐N at rest and during recovery indicated the metabolic importance of these N‐wastes. Hemolymph glutamate, glutamine, and PNH3 did not change. Hemolymph ammonia‐N, urea‐N, and urate‐N concentrations increased after exercise and more moderately after emersion, with urate‐N exhibiting the largest absolute increments, and urea‐N the longest‐lasting elevations. All three N‐wastes were present in the BCF, with ammonia‐N and PNH3 far above hemolymph levels even at rest. BCF volume declined by 34% postemersion and 77% postexercise, with little change in osmolality but large increases in ammonia‐N concentrations. Neither rapid flushing of stored BCF nor clearance of hemolymph ammonia‐N could explain the surges in ṀAmm after return to seawater. Research Highlights: In addition to continuous ammonia‐N excretion, intermittent urea‐N and urate‐N excretion are important components of the nitrogen metabolism of the green crab when in seawater. Excretion of all three continues during air exposure, but at reduced rates. After both exercise in air or quiet emersion in air, crabs exhibit elevated hemolymph ammonia‐N, urea‐N, and especially urate‐N. Branchial chamber fluid (BCF) volume is reduced, but its osmolality barely changes; its ammonia‐N levels increase above those in the hemolymph, while urea‐N and urea‐N do not. Upon return to seawater, massive, short‐lived increases in ammonia‐N excretion occur, but these do not appear to result from either flushing of BCF or clearance from the hemolymph. [ABSTRACT FROM AUTHOR]

The alien Asian date mussel Arcuatula senhousia inhabits several coastal environments worldwide. This species can form dense mats where individuals attach through byssus threads, thus altering the structure, functioning and biodiversity of the native communities. We investigated the feeding preference of different predators on this alien species in a Mediterranean coastal lagoon. To do this, a mesocosm experiment was conducted using two crab species (the Mediterranean green crab Carcinus aestuarii) and the Say mud crab Dyspanopeus sayi, and one gastropod, the banded dye‐murex Hexaplex trunculus as predators of A. senhousia with or without byssus mats. Our data suggest that C. aestuarii is a more effective predator against A. senhousia than D. sayi, and that H. trunculus is almost ineffective. A possible implication of this result is the potential use of the native crab C. aestuarii for limit the formation of the byssus mats, thus mitigating their potential negative effects on the native communities. [ABSTRACT FROM AUTHOR]

We examined the potential of North American river otters (Lontra canadensis) to buffer the expansion of the invasion by green crab (Carcinus maenas) on the West Coast of the United States, documenting the diet of otters from scat remains on the Wa'atch and Tsoo-Yess Rivers, in Washington State, in 2018 and 2019. We tallied hard remains of prey and calculated frequency of occurrence, and we compared predation of the green crab to monthly values of catch per unit of effort for this crab species. North American river otters did not consume green crab in the Tsoo-Yess River and infrequently consumed green crab in the Wa'atch River (1.66% frequency of occurrence), likely because of the lower abundance of the green crab compared to the abundance of other prey in these rivers. Although our results indicate that North American river otters were not a biotic control of green crab, future studies on the population status of the green crab and North American river otter in both rivers and the long-term predator-prey dynamics could help to better gauge the potential for biotic resistance in populations of the green crab. [ABSTRACT FROM AUTHOR]

On 2 September and 7 October 2022, we captured post-copulatory pairs of Callinectes sapidus (Blue Crab) in Green Crab traps in Great Bay Estuary, NH. On the first occasion, the 2 crabs included a mature post-ecdysis (12–24 hour) female and a mature male, and the female’s shed exoskeleton also remained in the trap. Both seminal receptacles had pink sperm plugs and were turgid with spermatophores, indicative of recent successful insemination. Details of the second capture mirrored the first with the exception that the exuvia was not in the trap. This is the first scientific reporting of Blue Crabs mating in Great Bay Estuary, NH, documenting an ongoing range expansion of a species with the potential to have major ecological and economic impacts. [ABSTRACT FROM AUTHOR]

Here we report on the long-term monitoring of Carcinus maenas (European Green Crab) populations on an intertidal region of a cobble beach in Maine conducted from 2011 to 2021. The number of Green Crabs collected fluctuated between 129 and 474 individuals per sample event. We collected crabs twice each year, with a total number collected of 389 to 798 per year. In addition, we collected Hemigrapsus sanguineus (Asian Shore Crab) in 2 sample years (2019 and 2021), accounting for only 7 individuals. No compelling relationships between Green Crab densities and sea-water temperature, average carapace width, or year of the collection were revealed. [ABSTRACT FROM AUTHOR]

Introduction: All decapod crustaceans are considered potentially susceptible to White Spot Syndrome Virus (WSSV) infection, but the degree of White Spot Disease (WSD) susceptibility varies widely between species. The European shore crab Carcinus maenas can be infected with the virus for long periods of time without signs of disease. Given the high mortality rate of susceptible species, the differential susceptibility of these resistant hosts offers an opportunity to investigate mechanisms of disease resistance. Methods: Here, the temporal transcriptional responses (mRNA and miRNA) of C. maenas following WSSV injection were analysed and compared to a previously published dataset for the highly WSSV susceptible Penaeus vannamei to identify key genes, processes and pathways contributing to increased WSD resistance. Results: We show that, in contrast to P. vannamei, the transcriptional response during the first 2 days following WSSV injection in C. maenas is limited. During the later time points (7 days onwards), two groups of crabs were identified, a recalcitrant group where no replication of the virus occurred, and a group where significant viral replication occurred, with the transcriptional profiles of the latter group resembling those of WSSV-susceptible species. We identify key differences in the molecular responses of these groups to WSSV injection. Discussion: We propose that increased WSD resistance in C. maenas may result from impaired WSSV endocytosis due to the inhibition of internal vesicle budding by dynamin-1, and a delay in movement to the nucleus caused by the downregulation of cytoskeletal transcripts required for WSSV cytoskeleton docking, during early stages of the infection. This response allows resistant hosts greater time to fine-tune immune responses associated with miRNA expression, apoptosis and the melanisation cascade to defend against, and clear, invading WSSV. These findings suggest that the initial stages of infection are key to resistance to WSSV in the crab and highlight possible pathways that could be targeted in farmed crustacean to enhance resistance to WSD. [ABSTRACT FROM AUTHOR]

Pollution, biological invasions and climate change pose the greatest threats to biodiversity worldwide. Few studies explore the interlink between invasive species and local pollution sites. This study describes the type and cytochemical properties of haemocytes from invasive Carcinus maenas on the southwestern Atlantic coast (Argentina). Moreover, the morphology of haemocytes and the total haemocyte count (THC) as well as the differential haemocyte count (DHC) of crabs sampled at clean or unpolluted and polluted sites were compared, to determine whether environmental stresses were evident in their haemocytes. Our results revealed two groups or subpopulations of haemocytes: hyalinocytes, as well as granulocytes and semi-granulocytes. The type of haemocyte from crabs from both sites showed no differences in their morphology. For cytochemical assays, only neutral red dye showed a more intense staining of crab haemocytes at the polluted site. All haemocytes were positive to Periodic Acid-Schiff and Sudan Black. THC of crabs from the clean site were significantly higher, as well as having a significantly higher proportion of hyalinocytes and a lower proportion of granular cells. This study provides a baseline immunological assessment for C. maenas haemocytes, suggesting a differential haemocytic response to environmental stress. [ABSTRACT FROM AUTHOR]

To evaluate the physiological ability to adjust to environmental variations of salinity, Carcinus maenas were maintained in 10, 20, 32 (control), 40, and 50 ppt (13.8 ± 0.6 °C) for 7 days. Closed respirometry systems were used to evaluate oxygen consumption ( M ˙ O 2 ), ammonia excretion (Jamm), urea-N excretion (Jurea-N) and diffusive water fluxes (with 3H2O). Ions, osmolality, metabolites, and acid–base status were determined in the hemolymph and seawater, and transepithelial potential (TEP) was measured. At the lowest salinity, there were marked increases in M ˙ O 2 and Jamm, greater reliance on N-containing fuels to support aerobic metabolism, and a state of internal metabolic alkalosis (increased [HCO3−]) despite lower seawater pH. At higher salinities, an activation of anaerobic metabolism and a state of metabolic acidosis (decreased [HCO3−] and increased [lactate]), in combination with respiratory compensation (decreased PCO2), were detected. TEP became more negative with decreasing salinity. Osmoregulation and osmoconformation occurred at low and high salinities, respectively, with complex patterns in individual ions; hemolymph [Mg2+] was particularly well regulated at levels well below the external seawater at all salinities. Diffusive water flux rates increased at higher salinities. Our results show that C. maenas exhibits wide plasticity of physiological responses when acclimated to different salinities and tolerates substantial disturbances of physiological parameters, illustrating that this species is well adapted to invade and survive in diverse habitats. [ABSTRACT FROM AUTHOR]

Simple Summary: Decapod crustaceans are used extensively in laboratory experiments. Recently in the United Kingdom decapods have been included in animal care protocols. However, little is known about how captive conditions affect the survival and general condition of wild crustaceans. We used the green shore crab, Carcinus maenas, to investigate the effects of stocking density and shelter on survival and vitality indices during a 6 month period in the laboratory. Both stocking density and the presence of shelter did not affect survival, nor have a clear effect on vitality indices (limb loss, claw strength, 'blood' protein concentration, righting time, leg flare and retraction). However, vitality indices showed that crab condition was declining over time: this became most apparent after 8 to 11 weeks storage in the laboratory. This decline in condition was likely due to repeated handling of the crabs, rather than the stocking conditions, which apparently led to a cumulative stress and a deterioration in animal health. Bringing wild crustaceans into the laboratory and holding them, even with modest experimental manipulation, may result in high mortality rates. Researchers and animal care committees need to be aware that wild captive invertebrates will respond very differently to laboratory-bred vertebrates, and plan experiments accordingly. The wide geographic distribution, large size and ease of capture has led to decapod crustaceans being used extensively in laboratory experiments. Recently in the United Kingdom decapod crustaceans were listed as sentient beings, resulting in their inclusion in animal care protocols. Ironically, little is known about how captive conditions affect the survival and general condition of wild decapod crustaceans. We used the green shore crab, Carcinus maenas, to investigate the effects of stocking density and shelter on survival and vitality indices during a 6 month period in the laboratory. Neither stocking density nor the presence of shelter affected survival. Stocking density also had no effect on the vitality indices (limb loss, claw strength, BRIX, righting time, leg flare and retraction). The presence of shelter did affect the number of limbs lost and the leg retraction response, but had no effect on the other vitality indices. All vitality indices changed, and mortality increased over time, independent of treatment: this became most apparent after 8 to 11 weeks storage in the laboratory. This decline in condition may have been due to repeated handling of the crabs, rather than the stocking conditions. In support of this, untracked, non-handled (control) individuals sustained a 4% mortality rate compared with 67% mortality in experimental crabs during the 6 month period. Although simple experimental monitoring of crabs with biweekly vitality tests only produced transient short-term stress events, the repeated handling over time apparently led to a cumulative stress and a deterioration in animal health. Bringing wild crustaceans into the laboratory and holding them, even with modest experimental manipulation, may result in high mortality rates. Researchers and animal care committees need to be aware that wild captive invertebrates will respond very differently to laboratory-bred vertebrates, and plan experiments accordingly. [ABSTRACT FROM AUTHOR]